An introduction to Masekhet Yoma, and the events surrounding and on Yom HaKippurim in the Beit HaMikdash. Note the shift in orientation to that of the perspective of the kohanim. The first chapter opens with preparing of the kohanim for the day of Yom Kippur. Namely, separating from his home 7 days in advance, appointing understudies, and so on, within reason. Plus, the parah adumah (red heifer), the other korban for which the kohen would sequester for 7 days in advance. Also, the "mishmarot" of the kohanim.